Chapter III Huai 'an Communication Construction

Chapter III Construction of Engineering Infrastructure

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1. The basic construction of communication engineering includes five aspects: lightning protection, grounding, anti-static, equipment use environment preparation and cable laying.

2. When lightning strikes a building, about 50% of the lightning energy is transmitted to the adjacent building through various cables and metal pipes, and finally leaked to the earth.

3. The main characteristics of lightning are instantaneous large current and selectivity. Instantaneous large current: the discharge time is very short, about 60 microseconds, which mainly includes three processes: pilot discharge, main discharge and residual light discharge; Selectivity: mainly manifested in geological selectivity, facility selectivity and site selectivity.

4. Lightning can be divided into direct lightning, induced lightning and spherical lightning.

5. According to IEC 61024-1-1,natural lightning is mainly represented by lightning current. Generally speaking, it can be divided into three levels: 200KA, 150KA and 100KA.

6. Lightning protection zones mainly include LPZ0A LPZ0B LPZ 1 LPZ2 LPZ3, in which LPZ0A and LPZ0B are distinguished by rolling ball method.

7, external lightning protection (direct lightning) protection system is mainly composed of lightning rod, grounding downlead and grounding system.

8. The simplest and most convenient way to prevent the impact of lightning electromagnetic pulse on electronic equipment is shielding.

9. Equipotential lightning protection is to ensure that all facilities form an "equipotential island" when lightning flows, and its essence is to ensure that there is no voltage difference between conductive parts.

10, ESD is called electrostatic discharge in English and electrostatic discharge in Chinese.

1 1. The hazards of static electricity include electrostatic spark, component breakdown, electrostatic adsorption and electromagnetic pulse.

12, the basic control methods of static electricity are leakage, neutralization and shielding.

13. The computer room has four grounding modes: AC workplace, safety protection place, DC workplace and lightning protection place.

14, the general principle of communication station grounding design is the principle of equal voltage and equal potential.

15. The total grounding of the computer room of the communication center should follow the principle of common ground, and the grounding resistance should be less than 1 ohm.

16, the common grounding system consists of grounding grid, grounding lead-in, grounding collection line and grounding line.

17. Common grounding method is adopted for general engineering. The grounding resistance of the central machine room is less than 1 ohm, the grounding resistance of the remote machine room is less than 5 ohms, and the grounding resistance of outdoor equipment is less than 10 ohms.

Second, short answer questions

1, briefly describe the meaning of overvoltage and intrusion path? Overvoltage refers to the long-term voltage fluctuation phenomenon that the root mean square value of AC voltage rises at power frequency, exceeding 10% of rated value and lasting for more than 1 min. Path: When lightning strikes the outside of the building, the voltage on the grounding resistance will drop; When lightning strikes the outside of the building, the internal circuit of the building will induce overvoltage.

2. Briefly describe the classification, characteristics and hazards of lightning?

Classification: direct lightning, induction lightning and spherical lightning. Features: Instantaneous high current and selectivity. Hazard: Communication equipment is often interrupted by lightning strike in a large area for a long time, resulting in a lot of economic losses.

★3. Explain outdoor and indoor lightning protection methods?

Outdoor lightning protection: ① lightning protection belt configuration ② direct lightning protection system requirements ③ lightning protection connection ④ shunt.

Indoor lightning protection: ① shielding ② equipotential lightning protection ③ multilevel protection principle ④ lightning protection of power supply system ⑤ grounding.

4. Briefly describe the overall protective measures of communication network?

Overvoltage generation mechanism of interconnected devices Interconnected cables induce lightning overvoltage. Interconnected devices that are struck by lightning conduct lightning overvoltage through cables. When struck by lightning, two interconnected devices bounce back on the ground potential.

5. Briefly describe the general principle of lightning protection?

The position of the equipment in the equipment system; Incoming mode; Direct lightning protection; Classification of lightning protection measures; Level 1 lightning protection level; Final lightning protection level; Secondary lightning protection level; Typical lightning protection classification of power supply; Lightning protection classification of typical signals; Lightning protection network design; Equipotential bonding requirements; Equal voltage and equipotential principle; Design of grounding grid; The path of discharge current; Design of power supply network; Environmental conditions; Maintenance and inspection of lightning protection system.

6. Briefly describe the mechanism and characteristics of static electricity?

Generation of static electricity: electrostatic charging of objects, also known as electrostatic electrification. It is an electrostatic phenomenon that the positive and negative charges on objects are out of balance because of the contact (friction) between substances in different charging sequences. The reason for the uneven distribution of electrons is that electrons are off track by external forces, which contain various energies (such as kinetic energy, potential energy, thermal energy, chemical energy, etc.). ).

The characteristics of static electricity (1) appear on the surface of an object, because it will balance each other inside the object, but it is difficult to completely balance the surface of the object; (2) Static electricity is an electric charge, which has all the characteristics of electricity and will generate an electric field, which will have an impact on nearby substances; (3) When static electricity moves, it will generate current, and the magnitude of the current determines the degree of damage to the equipment.

★7. Briefly describe the hazards of static electricity and protective measures?

Hazards of static electricity: ① Component breakdown (hard breakdown and soft breakdown) ② Electrostatic spark ③ Electrostatic adsorption.

④ Electromagnetic pulse

Protective measures: ① Personal protection: Wear antistatic clothing, working cap and work shoes. ② Operation surface protection: use anti-static floor and desk mat; Operators wear anti-static bracelets. ③ Shielding and packaging protection: use low electrostatic dissipation containers during storage and transportation;

Anti-static packaging is used for device packaging.

★8. Write the measurement method of grounding resistance?

Measurement method of grounding resistance: The distance from the current electrode to the edge d 1 of the grounding grid is generally 4 ~ 5 times of the maximum diagonal length d of the grounding grid, so that the potential distribution between them presents a gentle cross section. In general, the distance d2 from the voltage electrode to the edge of the grounding grid is about 50% ~ 60% of the distance d 1 from the current electrode to the grounding grid. When measuring, move the voltage electrode three times along the connecting line between the grounding grid and the current electrode, and the distance of each movement is about 5% of d 1. If the resistance measured three times is close. If it is difficult to take 4d ~ 5d, in areas with uniform soil resistivity, d 1 can take 2D, and d2 can take d; In areas with uniform soil resistivity, D 1 can be taken as 3D.

★9. Briefly describe the environmental requirements of the computer room?

(1) The civil engineering of the machine room has been completed, the doors and windows are in good condition, the through hole is well sealed, and it is dry and waterless, which can prevent water from infiltrating into the room from the hole. No obvious dust; ② Anti-static measures must be taken in the computer room; ③ For the machine room with raised floor, there should be a steel base when installing the equipment, and the non-electroplating base should be painted with antirust paint; (4) The height of the computer room door is ≥2.2 m, and the width is ≥ 1.8 m, which does not hinder the handling of equipment. Indoor clear height ≥ 3m; (5) The bearing capacity of the floor must be greater than 500 kg/m2; ⑥ The machine room must be equipped with air conditioning and ventilation equipment, with the humidity adjustment range of 40% ~ 65% and the temperature adjustment range of15℃ ~ 30℃; ⑦ There should be three lighting settings in the machine room: general lighting, guaranteed lighting and emergency lighting; Today there should be no water supply, drainage, gas and fire pipes in the machine room; Pet-name ruby it is forbidden to store inflammable, explosive and other dangerous goods in the computer room, and must be equipped with effective fire fighting equipment; Attending the power sockets with different voltages in the machine room should be clearly marked; The machine room is equipped with smoke and temperature alarm devices, and its performance should be good.

★ 10. What are the specific requirements for the connection inside, between and outside the cabinet? Interconnection in the cabinet: ① Three short-circuit requirements: In order to ensure the equipotential between GND, BGND (in the early welding cabinet, but now it has been cancelled in the assembly cabinet) and PGND in the cabinet, short-circuit the terminal at the entrance of the cabinet to ensure that the whole cabinet becomes an equipotential body; ② Grounding of the frame: the frame is connected with the PGND terminal through a wire with a cross-sectional area of 6mm2, with one end of the wire screwed on the PGND terminal and the other end screwed on the frame through a fastening screw; ③ Grounding of the rack: The metal parts of the cabinet insert frame should ensure good electrical connection with the rack. Joints (screw holes, slideways, lifting lugs) should not be sprayed with insulating paint or treated with non-conductive oxidation, resulting in poor conductivity; ④ Grounding of cupboard door: There are grounding terminals and signs under the front door, back door and side door of the cabinet, which should be connected to the grounding terminals of the cabinet structure through connecting cables with cross-sectional area not less than 16 mm2.

Interconnection between cabinets ① Connection of adjacent racks: During field engineering installation, racks in the same row of cabinets should be closely connected by fastening bolts and gaskets. The circular surface with a diameter of 50mm around the fastening bolt connection hole on the side of the frame body should not be painted, and it must be treated with rust prevention and corrosion protection. Washers and nuts should also be tinned to ensure good electrical contact. ② Interconnection between cabinets at the top: In order to ensure the equal potential of cabinets in the same exchange module, the cabinets GND in the same exchange module should be interconnected at the top with copper wires. For engineering installation, equipotential interconnection should also be carried out if the cabinets of the same switch module are not adjacent or in the same row. The cross-sectional area of the interconnection line is 10 mm2, and the length should be as short as possible according to the needs of the actual project. ③ Interconnection of buses between cabinets: the ground of each cabinet of the same exchange module is interconnected by short buses, the cross-sectional area of which is not less than 2 mm2, the length of which is 200mm, and both ends of which are respectively connected to GND of adjacent cabinets. The number of short wires should be at least 6, evenly distributed from the top of the machine to the cabinet. For cabinets where the same switch module is not in the adjacent position or in the same row, since the bus cannot be interconnected by short wires, only the GND at the top of the cabinet needs to be interconnected by cables.

Cable connection when DC distribution box (junction box) is grounded outside the cabinet: ① cabinet measurement: one end of blue -48V cable is connected to the terminal marked "-48V" in the cabinet distribution box, one end of black BGND(RTN) cable is connected to the terminal marked "GND" in the cabinet distribution box, and one end of yellow-green protective grounding cable is connected to the terminal marked "PGND" in the cabinet distribution box. Tighten the fixing screws. ② Power supply test: the other end of the blue -48V cable is connected to the -48V negative pole of the DC distribution cabinet (or junction box) in the computer room, and the other end of the black BGND(RTN) cable is connected to the -48V positive pole of the DC distribution cabinet (or junction box). The cross-sectional area of connecting cables shall be calculated according to the maximum working current of the whole cabinet, and shall not be less than 16 mm2. During construction, the connecting cable should be as short as possible, and the other end of the yellow-green protective grounding cable should be connected to the PGND layer of the DC distribution cabinet (or junction box). The PGND grounding rod of DC distribution cabinet (or junction box) is connected to the protective grounding rod of the machine room through cables, and the cross-sectional area of the connecting cable should be not less than 35 mm2. The cross-sectional area of the protective grounding cable from the exchange cabinet to the DC distribution cabinet (or junction box) is equal to that of the-48V power supply cable. During construction, the cable should be as short as possible and cannot be coiled.

★ 1 1. What are the grounding requirements of the central computer room? ① Workplaces, communication equipment protection places and building lightning protection places share a grounding grid; Common grounding methods are composed of grounding grid, grounding lead-in, grounding collection and grounding wire. The grounding collection line and the grounding line are connected in a layer-by-layer radiation mode. (2) Lightning protection grounding should be based on the principle of equal voltage and equipotential, so that the grounded metal system is connected to lightning protection grounding; ③ The ground wire design of the communication building should arrange the topological structure reasonably; ④ The grounding design of communication building should be considered from the overall structure; ⑤ When lightning strikes, there may be a large surge current in MET, grounding grid, grounding downlead, power room and incoming connection device, and communication equipment should keep a certain distance from it, at least above 1m; ⑥ Reliable lightning arresters should be installed for power lines, signal lines and control lines. They are long or extend out of the room. The grounding wire of lightning arrester should be reliably connected to the nearest grounding branch line, and the grounding wire should be multi-strand copper wire with a length of not more than 0.5m；; ⑦ The main grounding wire (MET) should be installed in the power room, about 50mm away from the wall (ground and cylinder) and insulated from the wall; ⑧ Copper bars (VR, FEB, CEEB) with cross-sectional area not less than1.20m2 are generally used for grounding diversity lines; Pet-name ruby grounding collection line (such as MET, VR, FEB, CEEB, etc. ) should be welded connection, or with four bolts and spring washers fastening, bolt diameter should not be less than 8 mm; Attending all grounding wires connected to the grounding branch wires shall be fastened with copper wire heads, bolts and spring washers, and the bolt diameter shall not be less than 8 mm ..

Third, the noun explanation

① Electromagnetic compatibility: The equipment or system has the ability to work normally in the electromagnetic environment without causing unbearable electromagnetic interference to anything in the environment.

② Equipotential connection: the exposed conductive part and the external conductive part are electrically connected at basically the same potential.

③ Protective grounding: protective grounding of the cabinet and the metal shell of various equipment in the cabinet.

It is called protective grounding to connect the uncharged exposed conductive part of electrical equipment to the protective line (PE line) or the protective zero line (PEN line) according to the grounding form of the system.

④ Surge protector: a device with nonlinear characteristics, which is used to limit transient overvoltage and surge current in the line.

Ball rolling method: A solid ball with a radius of at least 20m rolls freely on the surface of the external lightning protection system, where the ball can touch, it may be directly struck by lightning, which is the protected area LPZ0A, and where the ball cannot touch, it will not be directly struck by lightning, which is the protected area LPZ0B.

⑤ Direct lightning: It is a rapid discharge phenomenon between charged clouds and a point on the earth.

⑥ Shunt: At the interface between outdoor and indoor, connect a suitable lightning arrester in parallel between the conductor and the ground. When the overvoltage wave generated by direct lightning or induced lightning on the line enters the room or equipment along these wires, the resistance of the arrester suddenly drops to a low value, which is close to the short circuit state, and the lightning current is diverted to the ground, thus blocking most of the lightning current from the outside.

⑦ Multi-level protection: From the LPZ0 level protection zone to the innermost protection zone, graded protection must be implemented to gradually reduce the overvoltage to the level that the equipment can bear.